We and others have recently found that activating mutations in the serine/threonine kinase BRAF may be found in as many as half of all pediatric low grade astrocytomas (LGA). The overarching goals of these studies are to characterize the role of mutant BRAF in these tumors and to identify other mutations that drive the formation of both low- and high-grade pediatric astrocytomas. Specifically, we propose to: Aim One: Use new paraffin-friendly genomic technologies to identify oncogenic mutations in pediatric astrocytomas. The ability to interrogate formaldehyde-fixed, paraffin-embedded archival tissues expands the available sample sets of these infrequent pediatric tumors by a factor of ten or more relative to fresh frozen tumor collections. We will use these technologies on a unique set of over 1000 archival tumor samples to address two important unresolved questions in the field. Specifically, (i) what are the recurrent mutations or amplifications in pediatric astrocytomas that lack BRAF mutations? and (ii) What are the mutations that co-occur with BRAF mutations? Aim Two: Use functional approaches to identify mutations that cooperate with activated BRAF in pediatric astrocytomas. Similarto what has been found in BRAF-mutant melanoma, we anticipate that other mutations cooperate with mutated BRAF in pediatric astrocytomas. We will use both candidate and unbiased approaches to identify such mutations through the transformation of neural progenitor cells. Aim Three: identify druggable signal generators that function upstream and downstream of BRAF n transformed neural progenitors. In the fullness of time, small molecule inhibitors of BRAF may be used for the treatment of BRAF mutant pediatric LGAs. However, multiple protein kinases have been shown to be co-activated in high-grade adult gliomas, and this is also likely to be the case in mutant BRAF-transformed pediatric astrocytomas. In this Aim, we will conduct kinome-wide genetic screens for kinases that can substitute for activated BRAF to dysregulate the proliferation of normal neural progenitor cells. This information will help define genes that may drive pediatric astrocytomas that lack BRAF mutations as well as defining potential mechanisms of resistance to the inhibition of BRAF. All three specific aims are supported by an Innovative Neuro Pathology Core and by shared technologies and reagents from Projects Two and Three.